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Add support for custom CRC seed and polynomials.

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This commit is contained in:
Natalia Portillo
2018-02-03 18:36:23 +00:00
parent 4f9d2fdb89
commit c06fc84348
3 changed files with 160 additions and 63 deletions
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71
DiscImageChef.Checksums/CRC64Context.cs
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@@ -37,22 +37,23 @@ using System.Text;
namespace DiscImageChef.Checksums
{
/// <summary>
/// Implements a CRC64 (ECMA) algorithm
/// Implements a CRC64 algorithm
/// </summary>
public class Crc64Context : IChecksum
{
const ulong CRC64_POLY = 0xC96C5795D7870F42;
const ulong CRC64_SEED = 0xFFFFFFFFFFFFFFFF;
public const ulong CRC64_ECMA_POLY = 0xC96C5795D7870F42;
public const ulong CRC64_ECMA_SEED = 0xFFFFFFFFFFFFFFFF;
readonly ulong finalSeed;
readonly ulong[] table;
ulong hashInt;
/// <summary>
/// Initializes the CRC64 table and seed
/// Initializes the CRC64 table and seed as CRC64-ECMA
/// </summary>
public Crc64Context()
{
hashInt = CRC64_SEED;
hashInt = CRC64_ECMA_SEED;
table = new ulong[256];
for(int i = 0; i < 256; i++)
@@ -60,12 +61,37 @@ namespace DiscImageChef.Checksums
ulong entry = (ulong)i;
for(int j = 0; j < 8; j++)
if((entry & 1) == 1)
entry = (entry >> 1) ^ CRC64_POLY;
entry = (entry >> 1) ^ CRC64_ECMA_POLY;
else
entry = entry >> 1;
table[i] = entry;
}
finalSeed = CRC64_ECMA_SEED;
}
/// <summary>
/// Initializes the CRC16 table with a custom polynomial and seed
/// </summary>
public Crc64Context(ulong polynomial, ulong seed)
{
hashInt = seed;
table = new ulong[256];
for(int i = 0; i < 256; i++)
{
ulong entry = (ulong)i;
for(int j = 0; j < 8; j++)
if((entry & 1) == 1)
entry = (entry >> 1) ^ polynomial;
else
entry = entry >> 1;
table[i] = entry;
}
finalSeed = seed;
}
/// <summary>
@@ -93,7 +119,7 @@ namespace DiscImageChef.Checksums
public byte[] Final()
{
BigEndianBitConverter.IsLittleEndian = BitConverter.IsLittleEndian;
return BigEndianBitConverter.GetBytes(hashInt ^= CRC64_SEED);
return BigEndianBitConverter.GetBytes(hashInt ^= finalSeed);
}
/// <summary>
@@ -104,8 +130,8 @@ namespace DiscImageChef.Checksums
StringBuilder crc64Output = new StringBuilder();
BigEndianBitConverter.IsLittleEndian = BitConverter.IsLittleEndian;
for(int i = 0; i < BigEndianBitConverter.GetBytes(hashInt ^= CRC64_SEED).Length; i++)
crc64Output.Append(BigEndianBitConverter.GetBytes(hashInt ^= CRC64_SEED)[i].ToString("x2"));
for(int i = 0; i < BigEndianBitConverter.GetBytes(hashInt ^= finalSeed).Length; i++)
crc64Output.Append(BigEndianBitConverter.GetBytes(hashInt ^= finalSeed)[i].ToString("x2"));
return crc64Output.ToString();
}
@@ -127,10 +153,19 @@ namespace DiscImageChef.Checksums
/// <param name="hash">Byte array of the hash value.</param>
public static string File(string filename, out byte[] hash)
{
FileStream fileStream = new FileStream(filename, FileMode.Open);
ulong localhashInt;
return File(filename, out hash, CRC64_ECMA_POLY, CRC64_ECMA_SEED);
}
localhashInt = CRC64_SEED;
/// <summary>
/// Gets the hash of a file in hexadecimal and as a byte array.
/// </summary>
/// <param name="filename">File path.</param>
/// <param name="hash">Byte array of the hash value.</param>
public static string File(string filename, out byte[] hash, ulong polynomial, ulong seed)
{
FileStream fileStream = new FileStream(filename, FileMode.Open);
ulong localhashInt = seed;
ulong[] localTable = new ulong[256];
for(int i = 0; i < 256; i++)
@@ -138,7 +173,7 @@ namespace DiscImageChef.Checksums
ulong entry = (ulong)i;
for(int j = 0; j < 8; j++)
if((entry & 1) == 1)
entry = (entry >> 1) ^ CRC64_POLY;
entry = (entry >> 1) ^ polynomial;
else
entry = entry >> 1;
@@ -148,7 +183,7 @@ namespace DiscImageChef.Checksums
for(int i = 0; i < fileStream.Length; i++)
localhashInt = (localhashInt >> 8) ^ localTable[(ulong)fileStream.ReadByte() ^ (localhashInt & 0xffL)];
localhashInt ^= CRC64_SEED;
localhashInt ^= seed;
BigEndianBitConverter.IsLittleEndian = BitConverter.IsLittleEndian;
hash = BigEndianBitConverter.GetBytes(localhashInt);
@@ -169,7 +204,7 @@ namespace DiscImageChef.Checksums
/// <param name="hash">Byte array of the hash value.</param>
public static string Data(byte[] data, uint len, out byte[] hash)
{
return Data(data, len, out hash, CRC64_POLY, CRC64_SEED);
return Data(data, len, out hash, CRC64_ECMA_POLY, CRC64_ECMA_SEED);
}
/// <summary>
@@ -182,9 +217,7 @@ namespace DiscImageChef.Checksums
/// <param name="seed">CRC seed</param>
public static string Data(byte[] data, uint len, out byte[] hash, ulong polynomial, ulong seed)
{
ulong localhashInt;
localhashInt = seed;
ulong localhashInt = seed;
ulong[] localTable = new ulong[256];
for(int i = 0; i < 256; i++)
@@ -202,7 +235,7 @@ namespace DiscImageChef.Checksums
for(int i = 0; i < len; i++)
localhashInt = (localhashInt >> 8) ^ localTable[data[i] ^ (localhashInt & 0xff)];
localhashInt ^= CRC64_SEED;
localhashInt ^= seed;
BigEndianBitConverter.IsLittleEndian = BitConverter.IsLittleEndian;
hash = BigEndianBitConverter.GetBytes(localhashInt);